The effects of thyroid hormones and beta adrenergic agonists on target tissues may be evaluated by noninvasive monitoring of cardiovascular function. New techniques have been developed and evaluated for this purpose. The QKD interval, i.e., the interval between the onset of ventricular depolarization and the arrival of the pulse wave at the brachial artery, provides a rapid, innocuous, precise, reproducible, noninvasive technique for evaluation of thyroid cardiovascular and/or catecholamine status. This has been used for diagnosis and monitoring of therapy for patients with thyrotoxicosis, hypothyroidism, pheochromocytoma, and in the titration of effects of beta adrenergic blockers such as propranolol. This method has now been applied to evaluate thyroid function in children with cystinosis, and appears to indicate that patients are generally euthyroid. This technique has been used to evaluate the effect of fasting on the thyroid status of patients with morbid obesity, and correlated with results of T4, T3, and reverse T3 measurements.